2012-08-28 Press release
Summer cooling: Scientists calculate northern Europe’s climatic history
Cross-section of two tree trunks: the scientists reconstructed the summer temperatures of Scandinavia over the last 2,000 years based on these tree rings like these. The width of the annual rings and the density of the wood are proxies for climatic changes. The number of rings indicates the age of the tree (Photo: HZG).
Changes in the orbit of the Earth around the sun are responsible for this long-term temperature trend on a millennial time scale. This is due to the fact that the orbit of the Earth around the sun controls the spatial and seasonal distribution of solar radiation.
For instance, the point at which the Earth is closest to the sun was in July approx. 10,000 years ago; today it is in January. On a geological time scale, these fluctuations are the pacemaker for the transition between climatic warm and cold periods.
The evolution of temperatures can also be reconstructed from tree rings in Scandinavia, because the density of annual tree rings is a proxy for past temperatures. With the help of rings of old pines conserved in North Scandinavian lakes, the international team of scientists could verify the long-term cooling trend of northern European summers over the last 2,000 years, similar to the one calculated with the computer simulations: 0.3 °C per millennium.
This long-term trend is accompanied by short-term temperature fluctuations, for example, related to the 20th century warming as a result of the anthropogenic greenhouse effect.
The team of scientists from Germany, Finland Scotland and Switzerland published their results in the journal ‘Nature Climate Change’.
Dr. Eduardo Zorita
Institute for Coastal Research
Phone: +49 (0)4152 87 1856